1. Field of the Invention
The present invention relates to the field of fire-resistant enclosures for electrical apparatuses or valves, particularly for electrical motor-operated valves.
2. Description of the Prior Art
Thousands of refinery and chemical plant fires are reported each year. The flow lines in many of these plants are provided with motor-operated valves whose purpose is to provide a controlled shut-down of the plant soon after a fire has started. In many of these fires there are failures of the electrical components either within electrical junction and switch boxes, or within motor-operated valves which render the motor-operated valves useless. Heat damage to insulated wires carried in conduits or cables to the motor-operated valve also renders shutdown systems inoperable. The problem confronting these industries is to protect these apparatuses from the fire for a sufficient period of time after the fire has started so that the apparatus can be used and operated to shut down the plant.
Fires in chemical and refinery plants generate temperatures of 1800-2000.degree. F., and a suitable fire protection system for a motor-operated valve must maintain the temperature around the valve much lower than this so that the valves remain operable. Various methods and apparatuses have been tried to protect valves, electrical apparatuses, and the conduits leading to them, including sprayed on coatings of insulated material and bags formed of insulating material.
These solutions are unsatisfactory. Sprayed on coatings have caused electrical motor failures. The coatings must be removed for routine maintenance and often are not replaced following such maintenance. Bags made of insulating material require lacing together after being placed on an apparatus. Often maintenance personnel do not replace a bag after maintenance is performed on an apparatus due to the time required to lace up the bag. A bag in place over a valve is either entirely or partially destroyed or removed when hit by a stream of water or chemicals which is being used to extinguish a fire. The bag is then useless if the fire is rekindled or if a "flashback fire" occurs. The Flamemaster insulated enclosure is an example of an unsatisfactory bag-type enclosure.